Modlisation systme de la thrapie photodynamique

A method for permanently dyeing hair is provided which includes subjecting the hair to a number of treatments, having a set time interval between each two consecutive such treatments, and wherein each treatment comprises contacting the hair for a period from about 5 seconds to about 3 minutes with a recently made mixture of an alkaline and an acidic composition, followed by a rinsing step. A shampoo or conditioner base is present in the alkaline and acidic compositions.